Conventionally, a tube pump drawing fluid from one end and discharging it from another by generating negative pressure is known. Since this type of pump is configured simple and compact, the pump is used in different types of apparatuses that involve the use of fluid.
For example, the tube pump is used in an inkjet recording apparatus (a liquid injection apparatus), which discharges (injects) ink (liquefied fluid) to a recording sheet through a nozzle of a recording head, forming an image on the sheet. The tube pump draws ink from the nozzle when the recording head is cleaned for ensuring a smooth operation of the recording head (for example, Japanese Laid-Open Patent Publications No. 2001-301195 and No. 7-253082).
As illustrated in FIGS. 19 and 20, in the tube pumps described in the aforementioned documents, a flexible tube 1 is accommodated in a cylindrical case 2. A roller 3 operates to press and squeeze the tube 1 against an inner wall 2a of the case 2. The position at which the tube 1 is pressed by the roller 3 constantly shifts from an upstream position to a downstream position of the tube 1. The tube pump thus generates negative pressure at an upstream section of the tube 1. The ink is thus drawn from the upstream section of the tube 1 and is discharged from the downstream side of the tube 1.
However, these tube pumps (Japanese Laid-Open Patent Publication No. 2001-301195 corresponds to FIG. 19 and Japanese Laid-Open Patent Publication No. 7-253082 corresponds to FIG. 20) include overlapped portions 1a, 1b, at which a certain portion of the tube 1 crosses and overlaps a different portion of the tube 1 inside or outside the case 2. This arrangement enlarges the space occupied by the tube 1, thus preventing the tube pumps from being formed compact.
Further, in some color inkjet recording apparatuses, two flexible tubes 1, one for color ink and the other for black, are provided integrally with each other. In this case, the tube pump has four overlapped portions 1a, 1b of the tube 1. The space occupied by the overlapped portions 1a, 1b is thus further enlarged, worsening the aforementioned problem.
To solve the problem, an opening 2b extends through a portion of the inner wall 2a of the case 2, as shown in FIG. 21. The tube 1 is passed through the opening 2b without forming overlapped portions. The ends of the tube 1 are then separated from each other without interfering with each other.
However, in this configuration, at a position corresponding to the opening 2b of the case 2 (as indicated by the broken line in FIG. 21), the roller 3 quickly moves from the downstream portion to the upstream portion along the outer circumferential surface of the tube 1. At this stage, since the two portions have greatly different surface conditions, a noise may be caused due to an impact between the roller 3 and the tube 1. Further, when the roller 3 proceeds from the downstream portion to the upstream portion, squeezing of the tube 1 by the roller 3 may become insufficient. If this is the case, the interior of the tube 1 may instantly become continuous, releasing the negative pressure. This problem equally occurs in the tube pump of Japanese Laid-Open Patent Publication No. 7-253082 (FIG. 20).